Spring elemnt for compensating axial play in a motor shaft of an electric motor

ABSTRACT

The invention relates to a spring element ( 10 ) for compensating for axial play in a motor shaft of an electric motor. The invention proposes embodying such a spring element ( 10 ) out of plastic and of one piece with a stop disk ( 12 ), which is connected via spring arms ( 14 ) to a support foot ( 16 ), and placing it, along with the support foot ( 16 ), onto a support sleeve ( 18 ) with which the spring element ( 10 ) can be press-fitted onto the motor shaft. The invention has the advantage that it eliminates the axial play in the motor shaft of an electric motor with a spring element ( 10 ) that is inexpensive to manufacture and easy to install (FIG.  1 ).

PRIOR ART

[0001] The invention relates to a spring element for compensating foraxial play in a motor shaft of an electric motor, as generically definedby the preamble to the main claim.

[0002] Motor shafts of known electric motors are supported with axialplay in a motor housing. The axial play in the motor shaft is necessarybecause of or also as a result of manufacturing tolerances. In addition,an axial play in the motor shaft and the motor housing is necessarybecause of the different thermal expansions of the motor shaft and themotor housing. The axial play in the motor shaft results in noise thatis partially a function of the position of the electric motor and inpart, leads to distinctly audible impact noises during changes in therotation direction of the electric motor. In addition, axial vibrationsof the armature can occur, which result in noise and increased wear.

[0003] For this reason, efforts have been made to compensate for theaxial play in the motor shaft through the use of spring elements. Thus,for example, U.S. Pat. No. 2,307,772 has proposed placing a convexspring washer onto the motor shaft as a spring element, which issupported against a motor shaft bearing and an armature that is affixedto the shaft and as a result, compensates for axial play in the motorshaft. However, a large number of parts is required in order to installthe spring washer. The spring washer is connected to two flat supportwashers and parts are provided, which secure the spring washer to themotor shaft in a non-rotatable, axially movable fashion. The knownspring element is therefore complex and expensive with regard tomanufacture and installation.

ADVANTAGES OF THE INVENTION

[0004] The spring element according to the invention, with the featuresof claim 1, has a stop disk with which it is axially supported, forexample against a shaft bearing of the motor shaft of the electricmotor. One or more spring arms are connected to the motor shaft and areof one piece with it, which exert a spring force in the axial directionon the motor shaft and as a result, eliminate the axial play in themotor shaft. The spring element according to the invention has theadvantage that it can be simply and inexpensively manufactured, forexample by injection molding it, in particular out of plastic. Anotheradvantage is the installation of the spring element according to theinvention by simply sliding a single part onto the motor shaft. With thespring element according to the invention, the motor shaft isprestressed axially with a small amount of force and is secured in aparticular position. Operating noise due to the axial play in the motorshaft is eliminated and noise during a change in the rotation directionis sharply reduced or possibly even eliminated. Axial vibrations of themotor shaft are also prevented. In addition, the spring elementaccording to the invention compensates for different thermal expansionsof the motor housing and motor shaft.

[0005] Advantageous embodiments and improvements of the inventiondisclosed in the main claim are the subjects of the dependent claims.

DRAWINGS

[0006] The invention will be explained in detail below in conjunctionwith an exemplary embodiment shown in the drawings.

[0007]FIG. 1 is a half-sectional view of a spring element according tothe invention; and

[0008]FIG. 2 is a simplified depiction of an axial section through anelectric motor with the spring element according to the invention fromFIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0009] The spring element 10 according to the invention shown in FIG. 1has an annular stop disk 12 which is connected to a hollow cylindricalsupport foot 16 by means of spring arms 14 that are distributed over thecircumference. The stop disk 12, the spring arms 14, and the supportfoot 16 are made of one piece by means of plastic injection molding. Intheir middle section, the spring arms 14 extend in the circumferencedirection and at both ends, they are bent at right angles into anaxially parallel direction; at their two ends, they transition in onepiece into the stop disk 12 and/or into the support foot 16.

[0010] Due to the elasticity of the spring arms 14, the stop disk 12 isconnected to the support foot 16 in an axially resilient fashion. Aspring constant of the spring arms 14 is low so that an axial springforce of the spring element 10 is slight.

[0011] The hollow cylindrical support foot 16 is stepped on its inside.By means of the support foot 16, the spring element 10 is placed with aslight press-fit onto a support sleeve 18 whose outer diameter isstepped. The support sleeve 18 is essentially comprised of brass in theexemplary embodiment shown, but it can also be made of a differentmetallic or non-metallic material, for example also of plastic. Thesupport sleeve 18 makes it possible to axially remove the spring element10 from an injection molding tool, not shown, after the injectionmolding; the support sleeve 18 reduces an inner diameter of the supportfoot 16 of the spring element 10 to a diameter of a motor shaft of anelectric motor. An inner diameter of the support sleeve 18 is less thanan inner diameter of the stop disk 12. In the axial direction, thesupport sleeve 18 protrudes through the support foot 16 in the directionof the stop disk 12; it constitutes an axial stop 20 for the stop disk12, which limits an axial spring path of the stop disk 12 in thedirection of the support foot 16. In this manner, the spring element 16has an axial stop 20 for the stop disk 12 separate from the spring arms14, which prevents the spring arms 14 from being plastically deformed,broken, or damaged due to material fatigue. The axial stop 20 isseparate from the spring arms 14; the axial spring path of the stop disk12 is not limited by the contact of the spring arms 14 against the stopdisk 12 and the support foot 16.

[0012]FIG. 2 shows an electric motor 22, whose motor shaft 24 isprovided, according to the invention, with the spring element 10 fromFIG. 1. The electric motor 22 is provided for use as a seat adjustingmotor for an electrically adjustable seat of a motor vehicle. Theelectric motor 22 has a cup-shaped motor housing 26 whose innercircumference has permanent magnets 28 affixed to it. The motor shaft 24is supported in rotary fashion at one end in a housing end wall 30 thatis of one piece with the motor housing 26 and is supported at its otherend in a housing cover 32, which is inserted into an open end of themotor housing 26. For the rotary support, spherical porous bearings 34,36 are slid onto the ends of the motor shaft 24 and are respectivelysecured in the housing end wall 30 and in the housing cover 32, each bymeans of a respective spring washer 38, 40. An armature laminationbundle 42 with a winding and a commutator 44 is attached to the motorshaft 24 in a non-rotating manner. Intrinsically known carbon brushes insliding contact with the commutator 44 have been left out of the drawingfor the sake of simplifying the depiction.

[0013] Between the commutator 44 and one of the two porous bearings 36,the spring element 10 according to the invention is press-fitted withits support sleeve 18 onto the motor shaft 24. The stop disk 12 of thespring element 10, which has a greater inner diameter than the supportsleeve 18, can move freely on the motor shaft 24. The support sleeve 18and the support foot 16 of the spring element 10 are oriented toward thecommutator 44; the spring arms 14 press the stop disk 12 with a slightinitial stress axially against the porous bearing 36. Due to the lowspring constant of the spring arms 14, the prestressing force or thespring force is slight and consequently, so is a friction between thestop disk 12 and the porous bearing 36 during rotation of the motorshaft 24. Due to the low friction, the wear and power loss are likewiselow.

[0014] The spring element 10 according to the invention, which securesthe motor shaft 24 of the electric motor 22 in the axial direction withinitial tension between the two porous bearings 34, 36, eliminates axialbearing play, prevents axial movements of the motor shaft 24, andcompensates for manufacturing tolerances and thermal expansiondifferences between the motor housing 26 and the motor shaft 24. Theaxial stop 20 limits a maximal possible axial movement of the motorshaft 24 counter to the spring force of the spring arms 14 so that evenwith a fracture of the spring arms 14 or an axial load on the motorshaft 24 that is greater than a spring force of the spring arms 14, anaxial mobility of the motor shaft 24 remains limited to a permissiblevalue that does not impair the functioning of the electric motor 22.

1. A spring element for compensating for axial play in a motor shaft ofan electric motor, characterized in that the spring element (10) has oneor more spring arms (14) and a stop disk (12), which is of one piecewith the spring arms (14).
 2. The spring element according to claim 1,characterized in that the spring element (10) has a support foot (16),which is of one piece with the spring arms (14) and which can be used tofasten the spring element (10) to the motor shaft (24).
 3. The springelement according to claim 1, characterized in that the spring arms (14)extend approximately in the circumference direction.
 4. The springelement according to claim 1, characterized in that the spring element(10) is made of plastic.
 5. The spring element according to claim 1,characterized in that the spring element (10) has an axial stop (20),which is separate from the spring arms (14) and limits a spring path ofthe spring element (10).
 6. The spring element according to claim 2,characterized in that the spring element (10 has a support sleeve (18)upon which the support foot (16) is placed.